Diaphragm chuck with stiffening flange



Jan. 28, 1958 G. HOHWART ETAL DIAPHRAGM CHUCK WITH STIFFENING FLANGE "F-il ed Dec. 19, 1955 n Mm W 7 2} Z Z i United States Paten DIAPHRAGM CHUCK WITH STIFFENING FLANGE George. Hohwart, Farmington, and Ernest F. Hohwart,

Detroit, Mich., assignors to N. A. Woodworth Compally, Ferndale, Mich., a. corporation of Michigan Application December 19, 1955, Serial No. 553,816

I 4 Claims. (Cl. 279-1) This. invention. relates to improved diaphragm chucks and. more particularly to improved diaphragms therefor.

Diaphragm. chucks generally comprise a mounting support; on which a flexible, resilient diaphragm is secured. The diaphragm. is usually annular in, shape and carries work-holding jaws angularly spaced upon its face. One edge of the diaphragm is rigidly secured, to the support, the other edge being axially movable toflex the diaphragm to vary-the, radial spacing; between the jaws.

Among the problems encountered in making diaphragms for diaphragm chucks, particularly for relatively large chucks, are. the. difficulties: of maintaining a desired accurate. alignment of the jaws, and of providing adequate gripping force for. thejawswithout unduly sacrificing flexibility of the diaphragm. The latter problem is particularly important when the chucks are to be used to handle relatively heavy Work-pieces. Increasing the thickness and weight of the diaphragm increases its stiffness and its gripping force, but also diminishes its flexibility so that itrequiresa greater operating force and also tends to rupture more readily when repeatedly flexed. Precise and accurate. alignment of the jaws when they are in their gripping position is essential for the proper performance of many functions of diaphragm chucks. Any skewing, or twisting; of the. diaphragm, even in the slightest degree, changes. the relative radial or axial positions. of the jaws and thus changes the position of a workpiece held by the jaws, cocking it angularly or displacing it radially from alignment with a predetermined axis. Such cocking or radial. displacement may readily result in commercially intolerable errors on work performed on the workpiece or. in. erroneous. readings when checking work previously done.

Accordingly, one object of the instant invention is to improve diaphragms for use in diaphragm chucks. Another object is to provide improved diaphragm chucks having relatively great workpiece holding forces, a relatively high degree of flexibility, and a high resistance to twisting and. skewing so that relatively heavy workpieces may be releasably held therein accurately and precisely in predetermined. positions.

These and. other objects arev accomplished by the instantinvention. which provides adiaphragm chuck including: an annular diaphragm having a, radially disposed flexible, resilient. portion and an axially disposed stiffening flange adjacent to the movable edge thereof; One edge of the diaphragm is rigidly affixed to the mounting plate of the chuck, the flangeadjacent to, the opposite, movable edge serving as, a stiffening member to. prevent skewing of the diaphragm. Additionally, the diaphragm is undercut to reduce the. thickness of portions thereof adjacent to the flange and to the fixed edge. The undercuts, or grooves localize flexing of the diaphragm to predetermined areas thereof. It. has; been, found that the flange not only prevents, twisting. and skewing of the diaphragm, but also increasesrthe; diaphragm gripping: force by a surprisingly lacgeafacton. Theincrease' in grippihgforceisunexpected 2,821,100 Patented Jan. 28, 1958 1y greater than the increase that may be realized by any other known method of stiffening the diaphragm.

The invention will be described in greater detail in connection with the drawing, of which:

Figure 1 is an elevational, cross sectional view of a diaphragm chuck including a diaphragm according to the invention;

Fig. 2 is an elevational cross sectional View of a portion of the chuck shown in Fig. 1 in flexed position but wherein the diaphragm does not include the aforementioned undercuts, or grooves; and

Fig. 3 is a similar view to Fig. 2 but illustrating adiaphragm having grooves in accordance with the instant invention.

The invention will be described herein in connection with a diaphragm chuck that may be mounted upon either a fixed or a movable support and that includes actuating means to flex the diaphragm. It should be understood, however, that diaphragms according to the invention may be mounted upon any convenient support and may be actuated by any convenient means. The mounting and actuating means shown and described in this application do not form essential parts of the instant invention. They are included for the purpose of completeness and to facilitate an understanding of the operation and advantages of diaphragms according to the invention. The diaphragms may, for example, be mounted upon simple, annular supports, and may be actuated by screw jacks, by lever systems, or by pneumatic or hydraulic motors mounted apart from the diaphragms.

A diaphragm chuck according to a preferred embodiment of the invention as shown in Fig. 1 comprises a mounting plate 10 which may be attached to a fixed support or a rotatable spindle by any known means such as screws or bolts (not shown) passing through mounting holes 11 in the plate. An annular diaphragm 12, to be described in greater detail hereinafter, is attached as by screws 14 to the mounting plate 10 along the periphery thereof. An annular cylinder wall member 21 having a peripheral flange 22 is alsomounted on the mounting plate 10 in coaxial alignment therewith and fastened thereto by the screws 24. The edge of the cylinder wall flange 22 that abuts the mounting plate 10 is preferably accurately machined and finished as is also its seating surface on the mounting plate so that an air-tight seal may be effected between the cylinder wall 21 and the mounting plate. The mounting plate 10 is preferably also provided with an annular ridge formed by a shoulder 26. to facilitate alignment of the cylinder wall 21 and to reinforce it radially. A rigid piston 30 is disposed between the mounting plate 10 and the cylinder wall 21. Plug stops 32 are positioned within angularly spaced holes 34 in the mounting plate 10 and in the cylinder wall 21 to restrict "ice the movement of the piston 30; An alignment hub 40 radial face of the hub 40 is provided with grooves 56 to allow the passage of a. fluid from the central portion of the hub into the cavity formed. between the piston and the cylinder wall 21. A tube. 53. is sealedthrough the plug 52 as by a gasket 38 so thatfluid such ascompressed air may be injected through the piston 30 and through: the grooves 56 of the hub 40 to. exert pressure on the front face of the piston. Seals 36. are provided aroundthe rim of the piston 30. and. aroundthe rim of the: hub

40 to. contain a fiuidwhen it isinjected under pressure into the cavity formed by the piston 30, the cylinder wall 21 and the hub 40. A second tube 60 is sealed through the mounting plate 10. Conveniently, this tube 60 is positioned coaxially with and surrounds the first tube 58. Thus, only one stationary seal is required, whereas if the tubes 58 and 60 are separately sealed through the mount ing plate 10, a movable, or flexible seal must be provided for the tube 58 in order to allow for movement of the piston.

In operation, the piston may be either advanced or retracted by the introduction of a fluid such as compressed air into either the inner tube 58 or the outer tube 60. In its advance position the piston 30 is repelled away from the mounting plate 10, and when retracted it is drawn toward the mounting plate. The control of the supply of fluid to the respective tubes may be provided by any known means (not shown) such as a standard two-way valve.

The diaphragm 12 includes a relatively heavy peripheral flange 26 through which the screws 14 penetrate to fasten the diaphragm securely and firmly upon the mounting plate. According to the invention, the diaphragm is also provided with an inner flange 18 which serves to stiffen its inner edge to maintain the inner edge at all times substantially in a single plane. The radial portion of the diaphragm extends inwardly beyond the flange 18 to form a lip 16 which may be advanced or retracted as desired by the face plate 46. The outer rim of the face plate is notched to form a lip 64 that fits under the corresponding lip 16 of the diaphragm and presses against the diaphragm when the face plate is advanced. Backward pressure on the diaphragm is provided by a peripheral ring 61 fastened to the forward face of the face plate 46 by the screws 62 and projecting radially around the periphery of the face plate beyond the forward edge thereof and over the lip of the diaphragm. Thus, when the face plate 4-6 is retracted it exerts a positive retractive force upon the inner lip of the diaphragm.

It may be noted at this point that the retractive action of the face plate 46 against the diaphragm 12 is not generally required unless the chuck is used to hold relatively large workpieces or to hold workpieces against relatively strong operating forces. In many cases the natural elasticity of the diaphragm 12 provides adequate holding force to retain a workpiece securely between the jaws 66 when the diaphragm 12 is in its normal position and not stressed by the actuating mechanism. In chucks to be used on relatively light work, therefore, the peripheral ring 61 may be omitted, and the diaphragm may be flexed by power applied only to advance its inner edge, retraction being eflected by the elasticity of the diaphragm itself.

Clamping jaws 66 may be mounted upon the diaphragm 12 by means of mounting blocks 68. The mounting blocks are aligned upon the diaphragm by alignment pins 70 and secured to the diaphragm by screws 72. When the piston 30 is advanced by the application of fluid pressure upon the rear face of the piston, the face plate 46 drives the inner edge of the diaphragm 12 forward and flexes the diaphragm forwardly so that the jaws 66 are displaced and moved apart. Subsequently, when the piston is retracted, the diaphragm is permitted to return to its normal, unfiexed position and, moreover, its return to this position is insured by the application of a positive retracting force against the inner edge of the diaphragm by the peripheral ring 61.

Additionally, the diaphragm 12 is undercut to form grooves 17 and 19 as shown in greater detail in Fig. 3. The grooves serve to reduce the thickness of portions of the diaphragm adjacent to the two flanges 18 and 20 and are preferably disposed on the inner face of the diaphragm as shown. The inner flange so stifiens the diaphragm that when the grooves are omitted and the diaphragm is made of uniform thickness along its entire radial dimension, its bending curve is displaced outwardly as shown in Fig. 2

and the flexing of the diaphragm causes the mounting blocks 68 to rock and creep, thus straining the connections between the mounting blocks and the diaphragm. The strains induced by flexing the diaphragm are often sufiicient to damage the threads of the mounting block fastening screws 72 and may even break the screws. Furthermore, if the diaphragm is not provided with grooves its fiexure produces movement known as rock and creep between the mounting blocks 68 and the diaphragm so that the mounting blocks abrade the diaphragm and weaken it. By reducing the thickness of the diaphragm closely adjacent to the flanges 18 and 20 it has now been found possible to stiffen the inner edge of the diaphragm sufiiciently to maintain the work-holding jaws accurately in a predetermined spaced relationship without adversely affecting the working life of the assemblies.

The exact positions of the undercuts 17 and 19 are not critical in the practice of the invention. They may be placed on either the rear or the forward face of the diaphragm. One may be in any radial position between the mounting blocks 68 and the stiffening flange 18, and the other may be in any radial position between the mounting blocks 68 and the fixedly supported edge 20 of the diaphragm. It is only necessary that the thickness of two annular portions of the diaphragm be reduced, one reduced portion being disposed between the mounting blocks and the inner edge of the diaphragm, and the other reduced portion being disposed between the mounting blocks and the outer edge of the diaphragm. The flexing of the diaphragm is restricted to these reduced-thickness, annular portions, and strains induced between the mounting blocks and the diaphragm are minimized.

The stiffening flange 18 also may be varied in position. It may be extended forwardly of the diaphragm as well as or instead of rearwardly as shown herein. Further, in those diaphragms adapted to be fixedly mounted at their inner edges, the flange 18 should be transferred to the outer edge where it functions in the same manner.

The practice of the invention is particularly advan-' relatively thin material.

What is claimed is:

1. A diaphragm chuck having an essentially thin flexible and resilient diaphragm provided with a central opening three radially spaced, consecutively contiguous annular portions and a continuous annular stiffening flange along one edge thereof, the other edge of said diaphragm being adapted to be securely affixed to a rigid support, the central one of said three annular portions providing a mounting for work clamping jaws of said annular portions.

2. In a diaphragm chuck of the type having means to mount an annular flexible diaphragm rigidly along one edge thereof, and means to move the other edge of said diaphragm axially with respect to said one edge, the improvement comprising an annular essentially thin, flexible and resilient diaphragm mounted on said mounting means and having a continuous annular stiffening flange adjacent to the movable edge thereof, an annular portion of said diaphragm adjacent to said flange being of reduced thickness relative to the thickness of other portions of said diaphragm, another annular portion of said diaphragm adjacent to the rigidly mounted edge thereof being also of reduced thickness relative to the thickness of other portions of said diaphragm, and the portion of the diaphragm between said reduced portions providing a mounting surface for work clamping jaws.

3. In a diaphragm chuck, an essentially thin, flexible and resilient diaphragm having a central opening, the outer edge of said diaphragm being adapted to be securely aflixed to a rigid support, the inner edge of said diaphragm having a continuous annular stiffening flange, the thickness of said radial portion being reduced relative to its average thickness in a first predetermined region adjacent to said flange and in a second predetermined region adjacent to said outer edge.

4. An annular essentially thin flexible and resilient diaphragm for use in a diaphragm chuck having two concentrically disposed flanges, the first one of said flanges being disposed around the outer edge of said diaphragm, the second one of said flanges being disposed around the inner edge of said diaphragm, the thickness of said diaphragm being reduced relative to its average thickness in predetermined, spaced regions adjacent to said flanges.

References Cited in the file of this patent UNITED STATES PATENTS 

